There is increasing evidence that circadian rhythm disturbance can cause a variety of health disorders [1,2]. Nurses, because of their profession, have to perform their important and difficult tasks at any time in the 24 hours of the day. Erratic working shifts can cause decreased proficiency, somatic and psychological disorders and increase in nursing and medical error [3,4].

Previous studies have addressed a variety of maladies associated with shift work, including gastrointestinal (GI) symptoms [5,6]. For example, a study showed that working in different shifts can harm the GI normal movements and cause disorders in excreting digestive enzymes and acid-alkaline balance [7]. These alterations may be caused by sleep disorders, as they have a negative correlation with last night's sleep quality in these subjects [8]. Furthermore, in an investigation designed by German researchers, peptic ulcer incidence was higher in shift-workers and night-workers [9]. In a study in Japan, conducted by endoscopy, peptic ulcer prevalence was higher in shift-workers (2.38%) than in day-workers (1.03%). Duodenal ulcer also had greater prevalence (1.37% and 0.69%, respectively) [10]. A study in Iceland showed that nurses working 16 hours in a morning-evening shift had more severe GI symptoms, possibly because of a lack of enough resting time between the end of the evening shift and the start of the morning one [11]. Another study identified correlations between GI symptoms and psychological disorders such as anxiety and depression [12].

To supplement the existing literature, we investigated GI symptoms in shift-work and day-shift nurses in a training hospital in Iran.

Worldwide, gastrointestinal disorders are common complaints in the general population and must be monitored by community health care organizations [14,15]. For this purpose, questionnaires can be very helpful because they are easy to use extensively, can gather a lot of information rapidly, and are relatively inexpensive (particularly in comparison to monthly check ups) [16-18].

In the present study, gastrointestinal complaints were reported by a very high proportion (81.9%) of shift-workers. This proportion was twice as large as that reported in a previous study in Korea [19]. This could be due to environmental factors, hospital organization, social factors, insufficient welfare facilities, inordinate hours of working or erratic shifts, or even perhaps inappropriate answers to various questionnaires. On the other hand, Scott and colleagues reported 75% of gastrointestinal complaints in night-workers [20].

In our population of nurses in Iran, the prevalence of GI symptoms was significantly higher in shift-work nurses than in day-shift nurses, which is consistent with findings in other geographical locations [11,12]. The causes of this difference, however, are not evident. Factors such as sleep disorders [21-23], inappropriate nutrition or irregularity in the timing of meals [24], and mental and psychological disorders [12] might be responsible for the higher incidence of GI symptoms.

Irregularity in the timing of meals was previously described and was attributed to lack of time, appetite disturbance and work stress [5,24]. This could cause the nurses to have more GI symptoms, but, surprisingly, in our study nurses with meal timing irregularity had fewer symptoms (p < 0.001).

We found that use of gastrointestinal medication was much more common among shift-work nurses than among day-shift nurses (p = 0.002; Table 4). One might speculate that shift workers have more problems than others and try to eliminate them by using drugs. However, quite a few shift workers in our population used NSAIDs. These medications are mainly used for musculoskeletal pain and can cause or worsen GI symptoms. Thus, perhaps greater use of NDAIDs may be responsible for the greater incidence of GI symptoms in shift-work nurses.

It was somewhat surprising that no particular symptom was more prevalent in shift-work nurses than in day-shift nurses (Table 1). However, in Bilski's study, defecation irregularity was the only complaint more prevalent in shift-work nurses, and the frequency of other complaints, such as diarrhea, non-specific pains and gastric ulcers, did not differ from that in day-shift nurses [24].

Gastrointestinal symptoms were higher in nurses under 40 years of age (p = 0.015). This age effect was also reported by Zhen Lu and colleagues [12]. One would expect aging to make people more prone to gastrointestinal disorders, but it was the younger group who reported more GI symptoms in our study. Perhaps younger nurses are more likely to volunteer to work above average working hours or on irregular shifts.

We have to note that our study has some limitations. We had difficulties finding nurses that only worked in morning shifts. As mentioned earlier, only 27 (16.8%) nurses had morning-only shifts. Our data were obtained from a single hospital, and we are considering collecting data from more hospitals nationwide in the future. Our study was cross-sectional and thus, necessarily, only descriptive. Prospective longitudinal studies must be carried out to evaluate the causes and long-term effects of GI symptoms in shift-work nurses.

The authors declare that they have no competing interests.

HRS and ARM participated in design, acquisition of data, analysis and interpretation of data, and manuscript preparation. Both authors read and approved the final manuscript.